We recently posted a 1926 membership list for the National League of Commission Merchants, along with some background materials on the organization. While the list only identifies the member company owners, it offers some interesting information about their business.
For example, the A. J. Lemkau Co., Inc. in New York City was a produce distributor with a specialty of Celery. All of the sudden, you've got a unique fact that you may not have known before. What I love about these kinds of clues is that they open up new ways to search newspapers of the time. Instead of just focusing on the name, you can search for any mentions of Lemkau and CELERY!
If you'd like to learn more about the National League of Commission Merchants of the United States, I've posted an NLCM Overview and also an NLCM Historical Sketch, both from this original document.